The invention relates to a roller press for the pressure treatment or compaction of granular material, having at least two rolls, configured as freely rotating rolls, which are respectively rotatably mounted in a machine frame via a shaft, are driven in counter rotation and are separated from one another by a roll gap, wherein the shafts of the rolls are accommodated in bearing housings movably disposed in the machine frame, and wherein in each case two bearing housings disposed on one side of the rolls and belonging to different rolls are connected to each other via at least one pressure cylinder.
For the centering of the roll gap in roller presses for the pressure treatment or compaction of granular material, the rolls of the roller press are generally held by large-sized hydraulic drives in their desired position in order that, on the one hand, the pressure in the roll gap between the rolls is maintained and, on the other hand, as a result of the centering, the parallelism of the boundary of the roll gap is maintained by the surface of the rolls. In this centering operation, the hydraulic drives operate with high force, both to maintain the parallelism of the roll gap and to maintain the pressure in the roll gap. To this end, in the simplest case a first roll is mounted as a fixed roll immovably in the machine frame in bearings, which for their part are fastened to brackets by bearing housings in a machine frame. In contrast, a second roll is mounted as a movable roll in bearings which are disposed in bearing housings arranged movably between two brackets of the machine frame. The hydraulic drives, for the relative positioning of the movable roll in relation to the fixed roll and for the maintenance of the pressure in the roll gap, apply high forces to the machine frame as a counter bearing, so that it is necessary to design the machine frame in appropriately stable construction.
In roller presses having rolls with a weight of up to 50 metric tons, an appropriately large dimensioning of the machine frame is necessary, so that, in a necessary and scheduled roll change, the logistics and handling of the machine frame are complex and possible only with appropriately large-sized cranes and disassembly aids.
In order to reduce the scale of the necessary dimensioning of the machine frame, it is proposed in DE 102005006090 A1 to configure both rolls of the roller press as a movable roll, wherein these two movable rolls are connected to each other via the bearings and the bearing housings and via hydraulic drives. The rolls, the bearings, the bearing housings and the hydraulic drives here form a closed system of forces which relieves the machine frame of load and which machine frame can thus be dimensioned smaller. This arrangement has proved itself in practice. Since in this roller press the closed system of forces is configured displaceably in relation to the machine frame, it is necessary to center the closed system of forces during operation in order that the roll gap does not drift during operation of the press. This centering is achieved by the use of an appropriately dimensioned hydraulic system. It is here necessary to control by control circuits the hydraulics, which, counter to the forces of the moving system of rolls, hydraulics and bearings, such as bearing housings, center the roll gap.
In a refinement of this roller press, in DE 102007059072 it is proposed to use a hydraulic double cylinder which is fastened to the machine frame. In this hydraulic double cylinder, two adjacent hydraulic chambers operate and are supported one against the other. Despite the forces which operate on the hydraulic system, that force of the hydraulic cylinder which acts upon the roll gap is not transmitted to the machine frame. For the centering of the roll gap, it is necessary however to provide by a multi-quadrant operation the hydraulic pressures necessary to generate the pressure in the roll gap.